The electric public utility companies have for many years supplied the electric power demands of the consumer in an efficient and reliable manner. In order to maintain this high standard of service, the utilities have continually monitored the changing needs of their consumers, and have with reasonable accuracy, projected in advance the expected power requirements of the area served by their system, and have added to the generating capability of the system as necessary to meet such demand.
In recent years, however, the population explosion, the unexpected development of new subdivisions and new industrial complexes in areas served by the system, and the development of new and varied types of power consuming devices, both in the home and in industry, have made the accurate projection of future consumption more difficult. In addition, the cost of adding the further generating and transmission capabilities to the system and the increased fuel and labor costs incurred in operating such systems, has risen significantly while the billing rate to the consumer has, by reason of commission regulations, increased somewhat more slowly. As a result of these and other problems, the utilities are seeking a method of obtaining the revenue necessary to provide the generating equipment required to supply the needs of the consumer while yet apportioning the cost of such equipment and the generated power on a fair and equitable basis.
As one possible solution to the problem a number of the utilities are considering the possibility of using demand metering in residential areas served by their system. Such method of metering is well known and has been used extensively in industrial areas. In systems using demand metering, the customer charge is based upon both the total amount of energy used in a given period, and the maximum amount of power called for during the billing period. Such method of billing is considered more equitable than the conventional billing which is based on watthour measurement along. That is, in any system the utility must provide equipment which will satisfy the maximum demand of the system even though such demand may occur during only limited periods of the day. The utility is thus forced to purchase and install equipment which has a generating and distribution capability significantly greater than that which is required for a major part of the day. There is an interest therefore in reducing the maximum demand load of the system.
Demand meters provide the company with the capability of billing each consumer in accordance with the amount such consumer contributes to the maximum demand on the system. Since lowering of the demand by a consumer will result in a smaller bill, the consumer is encouraged to reduce his power requirements by deferring certain loads. The reduction of the power used by each consumer in turn reduces the total demand, and results in a more efficient operating system.
While the use of demand metering is considered by a number of companies to be both desirable and equitable, the cost of changeover of a system to such form of metering is a serious deterrent to its proposed use. That is, the replacement of each residential watthour meter in a system with the more expensive combination demand and watthour meters available on the market would be most expensive. In addition to the high initial purchase cost of the combination meters, there is the further loss due to an inventory buildup of a large number of unused watthour meters.
In an effort to provide a more practical solution to the problem, certain of the meter manufacturers have offered conversion kits for use in refitting the existing watthour meters so as to operate as a mechanical combination meter. As a practical matter, such refit is preferably effected in the shop so that the meter may be tested for accuracy after such refit. In the use of such type kits, the installer must pick up the unit in the field and return the same to the shop for the purpose of rebuilding. After the meter has been rebuilt, the necessary tests must be made, and the modified meter is returned to the field as a replacement for a further watthour meter in the system.
In addition to the time and expense involved in travelling to and from the field location, there is the further time and expense required by reason of the replacement of an existing meter with a modified mechanical combination meter. That is, the watthour meter at the time of removal will have a reading which represents the energy consumed at the time of replacement, and the modified combination meter, having been used previously at a different location, will have a totally unrelated reading. It is therefore necessary at the time of replacement to make a record of the readings on both meters and to report such readings to the billing department. At the end of the billing period the billing department must then calculate the measurements made by both meters during the period so that the bill for the energy consumed during such period is accurate.
Other companies have proposed refit kits which are intended to be installed in the field. However, in some states, the public utility commissions require that any meter upon which the seal is broken be returned to the shop for test purposes. Further, refit in the field is difficult, time consuming and costly.
In addition to being time consuming and expensive, such kits are for the most part limited for use with the particular type of meter which is manufactured by the company which provided the kit. Since most public utilities use the meters of several different manufacturers, the problem still remains as to how the meters of the other manufacturers and the different vintages of any one manufacturer may be modified so that the entire system will be on a demand metering basis.
In yet another approach to the problem certain manufacturers have provided special meters which as purchased have special attachments to facilitate changeover of a watthour meter to a demand meter. One such meter is shown in U.S. Pat. No. 2,482,793. While such arrangement does facilitate the addition of a thermal demand metering to a watthour meter, the problems noted above with respect to refit kits (i.e., the need to open the meter in the field or shop, the loss of reading during conversion, the related reporting problems when meters are interexchanged, and the problem of testing when required) are also present in such arrangement. In addition, such arrangement will provide an answer for only those utilities which purchase such type of meter from the particular meter company which manufactures the same to replace the watthour meters which are presently installed.